This Symposium is scheduled to take place over four days and to address the following specific areas: (1) molecular biology of negative regulators, including inhibition of gene activation, antisense strategies to suppression of DNA and RNA synthesis and gene inactivation by homologous recombination; (2) cellular biology of negative regulators, including description and characterization of negative growth factor inhibitory molecules and inactivation of growth factor receptors; and (3) in vivo effects of negative regulators, including viral suppression of hematopoiesis, expression of "silencer" genes and inactivation of growth factors in transgenic animals, and clinical effects of cell cycle inhibitors in hemoglobinopathies and other disorders of hematopoiesis. In addition to plenary session presentations, workshops and poster sessions will provide the opportunity for young investigators to present data pertaining to each of these topics. Our long-term objectives is to review and explore novel approaches to understanding the regulation of hematopoiesis and to investigating the potential application of negative regulators of the control of hematopoiesis in vivo.